Because that is their roots, and unlike other developers they realized that if they released it on all platforms at the same time they would be getting a ton of negative feedback. Most PC gamers don't even know there is going to be a console version, so they can't use the "it's been consolized" argument, when in fact it has been. Face it, there is a huge contingent of PC gamers out there that cry about any multi-platform game, regardless of how absurd their complaints are.

Things like Alchemy changes, linear gameplay, reworked combat, the fact the game plays so well with a controller, etc. would all be fuel for the PC game fanboy to use against TW2 if a console version was released at the same time. Make the changes to the game, make it incredibly beautiful, and release it six months ahead of a console version and everyone praises you as the PC rpg savior. Do the same exact things, only release the 360 and PS3 version at the same time, and PC gamers will say you've sold out like Bioware and abandoned your PC fanbase.

So now developers are delaying their game to keep the PC fanbase quiet. That's a new one.